This invention relates to a variable displacement compressor of a piston type.
Such a variable displacement compressor comprises a piston reciprocally driven in a cylinder bore. The piston has suction and compression strokes which are alternatively repeated to compress a gaseous fluid such as a refrigerant gas. During the suction stroke, the gaseous fluid is sucked into the cylinder bore through a suction port and a suction chamber of the compressor. During the compression stroke, the gaseous fluid id compressed in the cylinder bore into a compressed fluid. The compressed fluid is discharged from the cylinder bore to a discharge chamber of the compressor. In this type of a variable displacement compressor, it is assumed that the compressed fluid has pressure pulsation when the compressed fluid has a flow rate which is relatively low.
For example, a variable displacement compressor is revealed in U.S. Pat. No. 6,257,848, filed on Aug. 20, 1999, by Kiyoshi Terauchi, for assignment to the present assignee, based on Japanese Patent Application No. 153,853 of 1999 filed on Jun. 1, 1999. The variable displacement compressor is provided with an opening control valve disposed in a main channel between the suction port and the suction chamber for variably controlling an opening area of the main channel.
Referring to FIG. 1, description will be made as regards the opening control valve included in a variable displacement compressor in an earlier technology. The opening control valve has a valve body 4 for opening and closing a main channel 3 between a suction port 1 and a suction chamber 2, a cavity 5 for slidably receiving the valve body 4, a return spring 6 arranged within the cavity 5, a communication path 7 for establishing communication between the cavity 5 and the suction chamber 2, and a communication path 8 formed in the valve body 4. The suction port 1 has a downstream end provided with a valve seat 1a for receiving the valve body 4 to be brought into contact therewith.
The above-mentioned variable displacement compressor is operable at a variable flow rate. At a high flow rate, a pressure difference between the suction port 1 and the suction chamber 2 is great. Therefore, a pressure difference between the suction port 1 and the cavity 5 communicating with the suction chamber 2 through the communication path 7 is great also. Thus, a difference between a primary pressure and a secondary pressure on primary and secondary sides of the valve body 4 is great. As a consequence, the valve body 4 is separated from the valve seat 1a to be retreated within the cavity 5 with the spring 6 compressed to a large extent. In this event, the opening area of the main channel 3 is increased. A refrigerant gas introduced from the suction port 1 passes through the main channel 3 increased in opening area to flow into the suction chamber 2. Then, the refrigerant gas presses and opens a suction valve 9 to flow into a cylinder bore 10.
At a low flow rate, the pressure difference between the suction port 1 and the suction chamber 2 is small. Therefore, the pressure difference between the suction port 1 and the cavity 5 communicating with the suction chamber 2 through the communication path 7 is small also. Thus, the difference between the primary pressure and the secondary pressure on the primary and the secondary sides of the valve body 4 is small. As a consequence, the valve body 4 compresses the spring 6 to a less extent so that the valve body 4 approaches the valve seat 1a. In this event, the opening area of the main channel 3 is reduced. A part of the refrigerant gas introduced from the suction port 1 flows into the suction chamber 2 through the main channel 3 reduced in opening area. On the other hand, the other part of the refrigerant gas flows through the communication path 8 formed in the valve body 4, the cavity 5, and the communication path 7 into the suction chamber 2. The refrigerant gas flowing into the suction chamber 2 presses and opens the suction valve 9 to flow into the cylinder bore 10.
At a very low flow rate, the pressure difference between the suction port 1 and the suction chamber 2 is very small. Thus, the primary pressure and the secondary pressure on the primary and the secondary sides of the valve body 4 are substantially balanced with each other, i.e., substantially equal to each other. Under a weak urging force of the spring 6 restored into a substantially unloaded condition, the valve body 4 is very close to the valve seat 1a to substantially close the main channel 3. The refrigerant gas introduced from the suction port 1 passes through the communication path 8 formed in the valve body 4, the cavity 5, and the communication path 7 to flow into the suction chamber 2.
At the low flow rate, pressure pulsation of the refrigerant gas caused by self-induced vibration of the suction valve 9 is attenuated during passage through the main channel 3 reduced in opening area or through the communication path 7 and the communication path 8 of the valve body 4. This suppresses a vibration noise of an evaporator produced by the pressure pulsation propagating from the suction port 1 through an external cooling circuit to the evaporator.
The opening control valve disclosed in the above-mentioned publication is disadvantageous in the following respect. At the very low flow rate, the substantial balance between the primary pressure and the secondary pressure on the primary and the secondary sides of the valve body 4 is lost in a suction stroke as a result of pressure loss during passage of the refrigerant gas through the communication path 8 of the valve body 4. On the other hand, in a compression stroke, the refrigerant gas does not flow through the communication path 8 of the valve body 4 so that the substantial balance between the primary pressure and the secondary pressure on the primary and the secondary sides of the valve body 4 is recovered. Under the circumstances, every time when the suction stroke and the compression stroke are alternately repeated, the valve body 4 repeatedly performs very fine movement alternately towards the cavity 5 and towards the valve seat 1a. Such repetition of fine movement of the valve body 4 induces the pressure pulsation of the refrigerant gas, which in turn causes a noise to be produced.
It is therefore an object of this invention to provide a variable displacement compressor of a piston type, which is capable of reducing generation of a noise resulting from repetition of fine movement of a valve body of the opening control valve at a very low flow rate.
Other objects of the present invention will become clear as the description proceeds.
According to an aspect of the present invention, there is provided a variable displacement compressor of a piston type, which comprises a suction port, a suction chamber, a main channel communicating the suction port with the suction chamber, a valve body movably placed adjacent to the main channel for variably controlling an opening area of the main channel, a fluid damper coupled to the valve body for damping vibration of the valve body, and a bypass channel formed outside of the fluid damper to communicate the suction port with the suction chamber.
According to another aspect of the present invention, there is provided a variable displacement compressor of a piston type, which comprises a suction port, a suction chamber, a main channel communicating the suction port with the suction chamber, a valve body movably placed adjacent to the main channel for variably controlling an opening area of the main channel, a fluid damper coupled to the valve body for damping vibration of the valve body, a bypass channel formed outside of the fluid damper to communicate the suction port with the suction chamber, a compressor housing defining the suction port and the suction chamber, and a valve case fixed to the compressor housing and defining the main channel, the valve body being movably held by the valve case, the fluid damper being formed between the valve case and the valve body.
According to still another aspect of the present invention, there is provided a variable displacement compressor of a piston type, which comprises a suction port, a suction chamber, a main channel communicating the suction port with the suction chamber, a valve body movably placed adjacent to the main channel for variably controlling an opening area of the main channel, a fluid damper coupled to the valve body for damping vibration of the valve body, a bypass channel formed outside of the fluid damper to communicate the suction port with the suction chamber, a compressor housing defining the suction port and the suction chamber, and a valve case fixed to the compressor housing and defining the main channel, the valve body being movably held by the valve case. In the variable displacement compressor, the suction port is cylindrical and extends in a predetermined direction, the valve case being placed in the suction port and having a cylindrical wall extending in the predetermined direction and a bottom wall connected to a suction chamber side of the cylindrical wall, the main channel being formed to the cylindrical wall, the valve body being fitted inside the cylindrical wall to be movable in the predetermined direction, the return spring being interposed between the valve body and the bottom wall to urge the valve body towards an open end of the cylindrical wall, the valve case having a stopping portion for stopping the valve body against the return spring, the fluid damper being formed between the valve body and the bottom wall to serve in the predetermined direction.